#include <iostream>
using namespace std;
#define int long long
 
const int N = 91;
int f[N];
 
signed main()
{
    f[1] = 1, f[2] = 2;
    for(int i = 3; i < N; ++i)
    {
        f[i] = f[i - 1] + f[i - 2];
    }
    int n = 0;
    while(cin >> n)
    {
        cout << f[n] << endl;
    }
    return 0;
}